1. Field of the Invention
The invention relates to a percussion tool, such as a drill hammer and/or impact hammer, having an internal combustion engine.
2. Discussion of the Related Art
Percussion tools, including drill hammers and/or impact hammers having an internal combustion engine, referred to hereinafter as hammers for short, are known in particular to be relatively heavy breaker hammers, with which work is carried out in a substantially vertically downward direction. Due to the internal combustion engine, a striking mechanism, in particular a pneumatic spring striking mechanism, can be driven via a transmission and acts on a tool, for example drill bit. In petrol hammers of this type, a cooling air fan driven by the crankshaft of the internal combustion engine is provided to cool the engine. The cooling air fan generates a cooling air flow, which is guided along the outer side of the engine housing, that is to say of the cylinder of the internal combustion engine, in particular along the cooling ribs provided on the outer side of the cylinder.
The striking mechanism driven by the internal combustion engine and provided to generate the working motion of the hammer may also be heated intensely due to the air compression, in particular if the striking mechanism is a pneumatic spring striking mechanism. To cool the striking mechanism, it is therefore known to provide an additional fan wheel, which generates a separate cooling air flow for the striking mechanism. Corresponding installation space has to be provided for this additional fan wheel, thus increasing the complexity of the construction.
The principle of active cooling with the aid of forced convection on the basis of cooling air flows, which have been generated by cooling fans, has proven its worth in practice. However, there may be a problem in the fact that the active cooling does not function if the device is switched off. In particular, individual components of the hammer, for example the cylinder, the exhaust gas system, or the striking mechanism, are heated very intensely during operation. If the hammer is switched off and cooling no longer functions, the heat present distributes throughout the entire device, and therefore components which were not heated to a large extent during operation are also heated considerably. The temperature differences within the hammer become balanced over time, which leads to undesired intense heating of previously cool components. The temperature of the device only decreases gradually, and slowly overall, to ambient level.
The tank, fuel-guiding parts, and also the carburetor are included in particular among the parts which are cooler during operation. These components heat up considerably once the device has been switched off, which increases the tendency for the formation of vapor bubbles in the fuel. Start-up of the engine if the device is hot and after only a short break can be impaired, which, at the least, restricts the comfort for the operator.
An impact tool having an internal combustion engine is described in CH 110 334 A. A flywheel has blade-like spokes, with which a forced cooling air flow is produced. The cooling air flow is drawn beneath a sleeve through grooves so as to cool the engine.
Another impact tool is described in GB 255 519, in which the exhaust gas of an internal combustion engine is diverted via a nozzle. The exhaust gas flow entrains a cooling air flow, which is guided via a sleeve to cool the engine.
A hammer having a protective hood is known from DE 30 35 351 A1, said protective hood covering the hammer above, at the front and at the sides. The engine is left open so as to allow cooling thereof. The protective hood is located on the whole at a distance from the actual hammer and is cushioned against the hammer by means of springs.
U.S. Pat. No. 1,934,935 A describes an internal combustion engine in which cooling ribs are enclosed by a casing. The casing has openings in its lower and upper regions, whereby cooling air can flow in through said openings and can exit therefrom.